Replenishment Ship, HMAS Sirius, has reportedly been sent to the Coral Sea to monitor Russian ships (Picture: Royal Australian Navy)

By Sarah Dean, and Sally Lee and Freya Noble (Daily Mail Australia)

A third Australian warship has arrived in the Coral Sea to monitor a Russian naval fleet that is heading towards the country to reportedly 'spy on' the G20 summit.

A defence spokesperson confirmed to Daily Mail Australia that HMAS Sirius ‘has been positioned’ alongside the four-strong Russian fleet that is led by a guided missile cruiser and followed by destroyer Marshal Shaposhnikov.

A tug boat called Fotiy Krylov and supply tanker Boris Butoma round out the second half of the Russian ships.

Australia already has two navy ships watching the Russian boats but on Friday morning a Defence spokesperson confirmed: ‘HMAS Sirius has been positioned to support HMA ships Parramatta and Stuart, which are currently conducting maritime surveillance patrols.’

A fleet of Russian warships are reportedly on their way into Australian waters (Picture: AP)

They revealed that ‘AP-3C Orion aircraft are also conducting maritime surveillance patrols’.

If even more backup against the Russian ships is needed, HMAS Sydney has been positioned in the South Queensland area ‘to be available to support G20 activities’.

‘HMAS Sydney is also available for maritime surveillance patrols as required,’ the spokesperson said.

Russia has made no request to port in Australia, and if it wishes to do so it would have to provide at least 48 hours’ notice.

However, Defence said at the moment – while outside Australian waters - ‘the movement of these vessels is entirely consistent with provisions under international law for military vessels to exercise freedom of navigation in international waters.’

The news comes on the same day as British Prime Minister David Cameron touched down in Sydney before flying on to Canberra to address Parliament. He will then move on to Brisbane for the G20 meeting of world leaders.

The Russian navy fleet heading for Australian waters is believed to be acting on orders to spy on leaders and officials at the G20 summit.

The four Russian ships are near Bougainville in the Coral Sea (Picture Daily Mail Australia)

While Russian President Vladimir Putin is expected to land in Brisbane on Friday night for the conference, The Australian reports US warships have been keeping a close watch on four Russian ships as they moved south near Japan.

Sources have told The Daily Telegraph they have already warned those attending the summit to be wary their conversations on phones or other communication devices may be monitored.

But the Russians aren't expected to stand alone in the act as one source says there will be others engaging in similar activity.

In light of information that a fleet of Russian ships are on their way to Australian waters, Mr Abbott has downplayed the apparent show of strength.

The move appears to be a show of force from Russia, whose leader Vladimir Putin met with Mr Abbott at the APEC leader's summit on Tuesday in Beijing.

The pair discussed the MH17 tragedy and Abbott demanded an apology and compensation for the victims of the doomed flight from Putin, citing a similar case where the US took these actions after accidentally shooting down an aircraft.

The prime minister said the journey had been planned for sometime, and while it was unusual, the move is not entirely unprecedented.

'Plainly it takes weeks, if not months, to deploy warships thousands of miles from your bases,' Mr Abbott said.

'So this Russian deployment into Pacific waters is something that has been a long, long time in preparation.

'It's not unusual for Russia to deploy naval elements when there are significant international events taking place.

'Certainly it is unusual for Russian naval elements to be in Australian waters.

'Unusual, not entirely unprecedented, but unusual.'

The Australian government has dispatched two navy frigates and a replenishment ship to intercept and monitor the fleet of Russian navy ships believed to be headed towards Australia's coast. (Picture. Royal Australian Navy)

'Putin has organised fleets in recent years when he goes to these summits,' Mr Fergus added, as he explained Putin's father was in the navy so there are strong family ties.

When Australian ships reach the Russian fleet Mr Fergus said there will be some 'polite engagement and navy discourse'.

But he stressed 'there should be no alarm about diplomacy happening on the high seas'.

It's not the first time Russian naval vessels have been present while an international summit is on.

Defence is directing further questions regarding the vessels to Russian authorities.

Abbott reportedly knew of a developing security threat to Australia when he left China earlier on Wednesday.

Putin is said to have ordered the fleet, and it has been instructed to 'show the flag' on Saturday morning, The Daily Telegraph reported.

A senior government source told The Daily Telegraph the intentions of the Russian leader were obvious.

'There is no doubt this is posturing, to show the power of the Russia fleet,' the source said.

While still south of Bougainville in the Coral Sea, the force could be outside of Brisbane by the weekend when the G20 summit will be held.

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